Hospital records, surveys and compensation claims are used to calculate how many casualties are unknown to the police.

Louise EllmanCredit:
Ian Nicholson/PA

The Department for Transport estimates there are up to 800,000 road casualties in Britain each year.

Steve Gooding, director of motoring research charity the RAC Foundation, said: "The key to understanding any situation is to be able to trust the numbers behind it.

"The positive news is that the worst accidents which cause the worst injuries are almost universally likely to come to police attention, and hence get recorded and analysed to help avoid similar events in the future.

"The biggest cracks come at the other end of the spectrum where cuts, bruises and sore necks go unreported. However, the validity of some of these injuries must be questionable, not least many of the 1,500 whiplash claims which the insurance industry deals with daily and is working with government to reduce."